There are a number of well-known processes for producing polymers. Examples include emulsion polymerization, suspension polymerization, solution polymerization and bulk polymerization. Each of these may be carried out by either continuous or batch polymerization methods. Continuous polymerization methods, particularly continuous bulk polymerization methods, typically provide resource and energy savings over corresponding batch polymerization methods.
A plug flow reactor is one type of vessel in which to carry out continuous bulk or continuous solution polymerization. In a plug flow reactor, the reactants flow from an input end of a reactor to an output end (sometimes referred to in the art as an “extraction end”). In a plug flow reactor, the residence time distribution of reactants is generally minimized, resulting in what is often termed “plug flow” or “piston flow”. In an ideal plug flow reactor any cross sectional sample taken perpendicular to the flow of reactants has a uniform residence time in the reactor. Of course, in the real world, some variation from this ideal is permitted in reactors that are still considered “plug flow” reactors.
One type of plug flow reactor is a “stirred tube reactor” (also known in the art as a “stirred tubular reactor”). Most stirred tube reactors have a shaft stirrer disposed within a reaction chamber.
Continuous polymerization carried out in a stirred tube reactor may have a number of drawbacks. For instance, the formation of stagnant fluid pockets (i.e., those portions of the reacting fluid that remain motionless) tends to occur in certain regions of the reaction vessel. These stagnant pockets can lead to non-uniform residence time and a broadening of residence time distribution. Furthermore, high viscosity polymers may tend to adhere to the surfaces inside the reaction chamber, leading to reactor fouling.